Wavelength Checker

ABSTRACT

A light conversion portion includes a conversion material that converts infrared light to visible light. A reflection portion is fixed to a position on a main substrate at which the reflection portion faces an output end of an optical waveguide chip on the side from which light is output to an external space. The reflection portion includes a reflection surface that faces the output end and is inclined with respect to a plane of the main substrate such that a reflection direction is toward the upper side of the main substrate. The reflection surface reflects near infrared light.

This patent application is a national phase filing under section 371 ofPCT application no. PCT/JP2019/044866, filed on Nov. 15, 2019, whichapplication is hereby incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present invention relates to a wavelength checker, and morespecifically to a wavelength checker for checking signal light ininspection for starting a passive optical network (PON) system orisolating a failure in the PON system, for example.

BACKGROUND

In an access-type PON (Passive Optical Network) system of opticalcommunication systems, a plurality of lights having relatively farwavelengths, such as 1.3 μm and 1.5 to 1.6 μm, may be used at the sametime.

According to NPL 1, in a GE-PON (G-PON) system that has already beenintroduced, a wavelength of 1260 nm to 1360 nm (only a Regular band isdescribed for the G-PON) is used for a signal (upstream signal) from auser to a station building. Also, in the G-PON system, a wavelength of1480 nm to 1500 nm is used for a signal (downstream signal) from thestation building to the user, and a wavelength of 1550 nm to 1560 nm isused for a downstream video signal.

In a 10G-EPON (XG-PON) system that is to be introduced in the future aswell, a wavelength of 1.3 μm and a wavelength of 1.5 to 1.6 μm will beused. In a NG-PON2 system for which standardization has recently beencomplete, a wavelength of 1524 nm to 1544 nm (Wide band) is used for anupstream signal, a wavelength of 1596 nm to 1603 nm is used for adownstream signal, and a wavelength of 1550 nm to 1560 nm is used for adownstream video signal. Note that a description of PtPWDM (Point ToPoint Wavelength Division Multiplex) overlay, which is optional, isomitted. In this system, wavelength-division multiplexing is performed,unlike the GE-PON (G-PON) and the 10G-EPON (XG-PON). Wavelengtharrangement of these systems is shown in FIG. 19 .

Incidentally, in a PON system such as the GE-PON, optical power ischecked in a test for starting the system. When the system shifts fromthe GE-PON to the 10G-EPON in the future, a larger number of variouswavelengths will be used. When a test is performed under suchcircumstances, if it is possible to check the wavelength, it is possibleto determine the type of a signal and easily isolate a failure, and workefficiency may be increased.

CITATION LIST Non Patent Literature

[NPL 1] Ryo Koma, et al., “Standardization trends regarding furtherspeed up of PON system”, NTT technical journal, August 2017, pp. 51-53.

SUMMARY Technical Problem

Incidentally, an optical spectrum analyzer is a means for measuring thewavelength. However, the optical spectrum analyzer includes a movableportion for detecting, with a detector, diffracted light obtained bymoving a diffraction grating, and therefore, the device is large andheavy, and is difficult to carry. There is also a disadvantage in that apower source of wo V is commonly necessary. As described above,conventionally, there is a problem in that it is not easy to check, forexample, whether or not signal light is coming, in inspection forstarting a PON system or isolating a failure in the PON system.

Embodiments of the present invention were made to solve the problemdescribed above, and have an object of making it possible to easilycheck the presence or absence of signal light when starting a PON systemor isolating a failure in the PON system, for example.

Means for Solving the Problem

A wavelength checker according to embodiments of the present inventionis a wavelength checker including: an optical waveguide chip; and alight conversion portion constituted by a conversion material thatconverts near infrared light to visible light, wherein the opticalwaveguide chip that is connected to an optical fiber includes an arrayedwaveguide diffraction grating and is mounted on a main substrate, areflection portion is fixed to a position on the main substrate at whichthe reflection portion faces a light emission end surface of the opticalwaveguide chip on the side from which light is output to an externalspace, the reflection portion includes a reflection surface that facesthe light emission end surface and is inclined with respect to a planeof the main substrate such that a reflection direction is toward theupper side of the main substrate, and the light conversion portion isarranged at the light emission end surface of the optical waveguide chipor in the vicinity of the light emission end surface of the opticalwaveguide chip on the inner side of the light emission end surface.

Effects of Embodiments of the Invention

As described above, according to embodiments of the present invention,the reflection portion is provided at a position at which the reflectionportion faces the light emission end surface, and the light conversionportion constituted by the conversion material that converts infraredlight to visible light is arranged at the light emission end surface ofthe optical waveguide chip or in the vicinity of the light emission endsurface of the optical waveguide chip on the inner side of the lightemission end surface, and therefore, it is possible to easily check thepresence or absence of signal light when starting a PON system orisolating a failure in the PON system, for example.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view showing a configuration of a wavelength checkeraccording to Embodiment 1 of the present invention.

FIG. 2A is a cross-sectional view showing a configuration of a portionof the wavelength checker according to Embodiment 1 of the presentinvention.

FIG. 2B is a cross-sectional view showing a configuration of a portionof the wavelength checker according to Embodiment 1 of the presentinvention.

FIG. 2C is a cross-sectional view showing a configuration of a portionof the wavelength checker according to Embodiment 1 of the presentinvention.

FIG. 2D is a cross-sectional view showing another configuration of aportion of the wavelength checker according to Embodiment 1 of thepresent invention.

FIG. 2E is a cross-sectional view showing a configuration of a portionof the wavelength checker according to Embodiment 1 of the presentinvention.

FIG. 2F is a cross-sectional view showing another configuration of aportion of the wavelength checker according to Embodiment 1 of thepresent invention.

FIG. 3 is a plan view showing a configuration of an arrayed waveguidediffraction grating.

FIG. 4 is a characteristic diagram showing a calculation result of atransmission spectrum of an arrayed waveguide diffraction grating in anoptical waveguide chip.

FIG. 5A is a perspective view showing a configuration of a wavelengthchecker according to Embodiment 2 of the present invention.

FIG. 5B is a side view showing a configuration of a portion of thewavelength checker according to Embodiment 2 of the present invention.

FIG. 5C is a plan view showing a configuration of a portion of thewavelength checker according to Embodiment 2 of the present invention.

FIG. 6A is a perspective view showing a configuration of a portion ofthe wavelength checker according to Embodiment 2 of the presentinvention.

FIG. 6B is a cross-sectional view showing a configuration of a portionof the wavelength checker according to Embodiment 2 of the presentinvention.

FIG. 7A is a cross-sectional view showing a method for manufacturing achild optical waveguide chip that constitutes the wavelength checkeraccording to Embodiment 2 of the present invention.

FIG. 7B is a cross-sectional view showing the method for manufacturingthe child optical waveguide chip constituting the wavelength checkeraccording to Embodiment 2 of the present invention.

FIG. 7C is a cross-sectional view showing the method for manufacturingthe child optical waveguide chip constituting the wavelength checkeraccording to Embodiment 2 of the present invention.

FIG. 7D is a cross-sectional view showing the method for manufacturingthe child optical waveguide chip constituting the wavelength checkeraccording to Embodiment 2 of the present invention.

FIG. 7E is a cross-sectional view showing the method for manufacturingthe child optical waveguide chip constituting the wavelength checkeraccording to Embodiment 2 of the present invention.

FIG. 8A is a cross-sectional view showing a configuration in thevicinity of a light conversion portion of the wavelength checkeraccording to Embodiment 2 of the present invention.

FIG. 8B is a cross-sectional view showing another configuration in thevicinity of the light conversion portion of the wavelength checkeraccording to Embodiment 2 of the present invention.

FIG. 9 is a characteristic diagram obtained by plotting expression (7).

FIG. 10 is a plan view showing a configuration of a portion of anotherwavelength checker according to Embodiment 2 of the present invention.

FIG. 11 is a plan view showing a configuration of a portion of the otherwavelength checker according to Embodiment 2 of the present invention.

FIG. 12 is a characteristic diagram showing a calculation result of atransmission spectrum of an arrayed waveguide diffraction grating in achild optical waveguide chip.

FIG. 13 is a characteristic diagram showing a calculation result of atransmission spectrum of an arrayed waveguide diffraction grating in anoptical waveguide chip.

FIG. 14 is a characteristic diagram showing a spectrum obtained bycompositing the spectrum shown in FIG. 12 and the spectrum shown in FIG.13 .

FIG. 15 is a plan view showing a configuration of a portion of awavelength checker according to Embodiment 3 of the present invention.

FIG. 16A is a plan view showing a configuration of a portion of thewavelength checker according to Embodiment 3 of the present invention.

FIG. 16B is a plan view showing a configuration of a portion of thewavelength checker according to Embodiment 3 of the present invention.

FIG. 17A is a characteristic diagram showing a calculation result of aspectrum of light that is input from a main first input waveguide of anoptical waveguide chip and is transmitted through an arrayed waveguidediffraction grating.

FIG. 17B is a characteristic diagram showing a calculation result of aspectrum of light that is input from a sub first input waveguide of theoptical waveguide chip and is transmitted through the arrayed waveguidediffraction grating.

FIG. 18 is a characteristic diagram showing a spectrum obtained bycompositing the spectrum shown in FIG. 17A and the spectrum shown inFIG. 17B.

FIG. 19 is an illustrative diagram showing a wavelength arrangementrelationship between NG-PON2, 10G-EPON (XG-PON), and GE-PON (G-PON).

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The following describes wavelength checkers according to embodiments ofthe present invention.

Embodiment 1

First, a wavelength checker according to Embodiment 1 of the presentinvention will be described with reference to FIGS. 1 and 2A to 2D.

The wavelength checker includes an optical waveguide chip 101. A knownarrayed waveguide diffraction grating is formed in the optical waveguidechip 101 (see Reference Document 1). The arrayed waveguide diffractiongrating includes a first arrayed waveguide 103, a first input-side slabwaveguide 104, a first output-side slab waveguide 105, a first inputwaveguide 106, and first output waveguides 107. FIG. 1 shows a plane ofthe wavelength checker. Note that the reference sign 151 denotes a mainsubstrate, the reference sign 109 denotes a reflection portion, and thereference sign 102 denotes a light conversion portion that isconstituted by a conversion material that converts near infrared lightto visible light. Also, the reference sign 161 denotes a fiber block,the reference sign 162 denotes an optical fiber, and the reference sign163 denotes a connector.

The first arrayed waveguide 103 is constituted by a plurality ofwaveguides that have a constant difference in optical path length. Thedifference between optical path lengths of two adjacent waveguides ofthe first arrayed waveguide 103 is constant. The first input-side slabwaveguide 104 is connected to a light input end of the first arrayedwaveguide 103. The first output-side slab waveguide 105 is connected toa light output end of the first arrayed waveguide 103. The first inputwaveguide 106 is connected to an input side of the first input-side slabwaveguide 104. A plurality of first output waveguides 107 are providedand are connected to an output side of the first output-side slabwaveguide 105.

The light conversion portion 102 is constituted by a conversion materialthat converts infrared light to visible light. The reflection portion109 is fixed to a position on the main substrate 151 at which thereflection portion 109 faces an output end (light emission end surface)108 of the optical waveguide chip 101 on the side from which light isoutput to the external space. Also, the reflection portion 109 includesa reflection surface 109 a that faces the output end 108 and is inclinedwith respect to a plane of the main substrate 151 such that a reflectiondirection is toward the upper side of the main substrate 151 (FIG. 2C).The reflection surface 109 a reflects near infrared light. Thereflection portion 109 can be constituted by metal such as aluminum oran aluminum alloy, for example. Also, the reflection surface 109 a canbe formed by mirror-finishing a surface of the reflection portion 109constituted by such a metal and facing the output end 108. Thereflection surface may also be constituted by a reflection film 109 bthat is formed by applying a coating material that reflects nearinfrared light, for example (FIG. 2D, FIG. 2E, FIG. 2F). In the casewhere the reflection film 109 b is formed, a surface of the reflectionfilm 109 b that faces the output end 108 can be said to be thereflection surface.

The light conversion portion 102 is arranged at the output end 108 ofthe optical waveguide chip 101 or in the vicinity of the output end 108of the optical waveguide chip 101 on the inner side of the output end108. The light conversion portion 102 is arranged at a position throughwhich guided light or emitted light passes in the vicinity of the outputend 108 of the optical waveguide chip 101. More specifically, the lightconversion portion 102 is not arranged on an optical path along whichlight emitted from the output end 108 travels until reaching thereflection surface 109 a, but is arranged on the optical path ofreflected light. Note that the light conversion portion 102 is formed soas to extend in a direction in which the plurality of first outputwaveguides 107 are arranged. The light conversion portion 102 extendsfrom one end to the other end of an array of the plurality of firstoutput waveguides 107, for example.

The conversion material is a phosphor or a fluorescent substance thatconverts near infrared light to visible light, for example. The lightconversion portion 102 can be obtained by mixing the conversion materialwith thermosetting silicone resin, and curing the resin through heating,for example. For example, a phosphor manufactured by LumitekInternational can be used. An example of the conversion material hassensitivity in a range of 700 nm to 1700 nm.

In the wavelength checker according to Embodiment 1, near infrared lightthat is demultiplexed according to wavelengths by the arrayed waveguidediffraction grating, guided through the first output waveguides 107, andemitted from, for example, the output end 108 reaches the lightconversion portion 102, and visible light is generated. The generatedvisible light reflects off the reflection surface 109 a (reflection film109 b) of the reflection portion 109 and is emitted toward the upperside of the main substrate 151, and accordingly, can be seen on theupper side of the main substrate 151. Also, the visible light isgenerated from a position that the emitted near infrared light reached,and therefore, it is possible to identify a first output waveguide 107from which the near infrared light is emitted, based on the position atwhich the visible light is generated. Since wavelengths of near infraredlights that are demultiplexed and guided through the respective firstoutput waveguides 107 are already known, it is possible to check thewavelength by checking the position at which the visible light isgenerated (seen).

Note that as shown in FIG. 2A, the first input-side slab waveguide 104is constituted by a lower clad layer 112 that is formed on, for example,a Si substrate 111 constituted by Si, a core portion 104 a that isformed on the lower clad layer 112, and an upper clad layer 113 that isformed on the core portion 104 a. Note that FIG. 2A shows a crosssection taken along a line a-a′ in FIG. 1 . Also, the main substrate 151under the Si substrate 111 is omitted in FIG. 2A.

Also, as shown in FIG. 2B, the first arrayed waveguide 103 isconstituted by the lower clad layer 112 formed on the Si substrate 111,a plurality of core portions 103 a that are formed on the lower cladlayer 112, and the upper clad layer 113 formed on the plurality of coreportions 103 a. Note that FIG. 2B shows a cross section taken along aline b-b′ in FIG. 1 . For example, the Si substrate 111 is a siliconsubstrate, each clad layer is constituted by quartz-based glass, and thecore portions 103 a and the core portion 104 a are constituted byquartz-based glass. Note that the main substrate 151 under the Sisubstrate 111 is omitted in FIG. 2B.

Here, as shown in FIG. 2C, the light conversion portion 102 can bearranged over the entire surface of the output end 108 of the opticalwaveguide chip 101. Also, the reflection portion 109 can be constitutedby a right-angle prism. The right-angle prism includes a surface that isarranged in contact with the main substrate 151, a surface orthogonal tothis surface, and a sloped surface that is adjacent to these twosurfaces and faces the output end 108. The sloped surface serves as thereflection surface 109 a. The reflection portion 109 is a columnar(triangular prism) structure of which the base is an isosceles righttriangle. FIG. 2C shows a cross section taken along a line c-c′ in FIG.1 . It is also possible to form the reflection film 109 b that serves asthe reflection surface, by applying a coating material that reflectsnear infrared light to the sloped surface of the reflection portion 109constituted by the right-angle prism (FIG. 2D).

Also, as shown in FIG. 2D, the light conversion portion 102 may bearranged in (fill) a groove 114 that is formed across optical waveguidesthat extend to the output end 108 of the optical waveguide chip. Thegroove 114 is arranged in the vicinity of the output end 108. In thiscase, near infrared light that is demultiplexed according to wavelengthsby the arrayed waveguide diffraction grating and is guided through thefirst output waveguides 107 reaches the light conversion portion 102 infront of the output end 108, and visible light is generated. Thegenerated visible light is transmitted through the first outputwaveguides 107 (the lower clad layer 112 and the upper clad layer 113)between the light conversion portion 102 and the output end 108, and isemitted from the output end 108. The visible light emitted from theoutput end 108 reflects off the reflection film 109 b of the reflectionportion 109 and is emitted toward the upper side of the main substrate151.

The groove 114 can be formed by dicing, etching, or the like. Forexample, the groove 114 can be formed using a known photolithographytechnique and dry etching technique. The light conversion portion 102 isobtained by filling the formed groove 114 with the conversion material.When the groove 114 is formed as described above, the length of thegroove through which light passes can be appropriately designed bydesigning a mask that is used in the photolithography technique. Byincreasing the length of the groove, it is possible to increase thedistance by which near infrared light passes through the lightconversion portion 102, to increase wavelength conversion efficiency.

Alternatively, as shown in FIG. 2E, it is also possible to make theoutput end 108 recessed from the output end 108 side end portion of theSi substrate in, and provide the light conversion portion 102 at theoutput end 108 on the end portion of the Si substrate in.

Alternatively, as shown in FIG. 2F, it is also possible to provide thelight conversion portion 102 at the output end 108 on an end portion ofthe Si substrate 111 similarly to the above case, and additionallyprovide a fixing member iota that is made of a transparent material suchas glass.

The following more specifically describes the arrayed waveguidediffraction grating. The following describes, as an example, a casewhere the first arrayed waveguide 103 is constituted by eightwaveguides, and there are eight first output waveguides 107. AlthoughFIG. 1 shows eleven waveguides, actually, the number of waveguides isgreater than eleven. In this arrayed waveguide diffraction grating,multiplexed light with eight wavelengths, which is input to the firstinput waveguide 106, diverges into eight outputs.

First, the multiplexed light that is input to the first input waveguide106 diffracts and spreads in the first input-side slab waveguide 104,and portions of the light respectively couple with the waveguides of thefirst arrayed waveguide 103 and are guided therethrough. The opticalpath length of the first arrayed waveguide 103 is long on the upper sideof the sheet of FIG. 1 (outer side), and decreases toward the lower sideof the sheet of FIG. 1 (inner side) by equal lengths. At the terminalend of the first arrayed waveguide 103, phase differences are generatedbetween the waveguides of the first arrayed waveguide 103 from the outerside waveguide to the inner side waveguide. Therefore, when the lightenters the first output-side slab waveguide 105, inclination of afan-shaped equiphase surface generated due to the shape of the slabwaveguide varies depending on the wavelengths, and the portions of lightare collected to (optically couple with) corresponding first outputwaveguides 107 according to the wavelengths. Thus,wavelength-division-multiplexed light can be separated (demultiplexed)according to the wavelengths by the arrayed waveguide diffractiongrating.

Note that, as shown in FIG. 3 , in a commonly used arrayed waveguidediffraction grating, an arrayed waveguide 501 is curved at a singlepoint like an arc in a plan view. In FIG. 3 , the reference sign 502denotes an input-side slab waveguide, the reference sign 503 denotes anoutput-side slab waveguide, the reference sign 504 denotes an inputwaveguide, and the reference sign 505 denotes output waveguides. Incontrast, in the arrayed waveguide diffraction grating according to theembodiment, the first arrayed waveguide 103 is curved at a plurality ofpoints in a plan view and has a shape like wings of a gull in a planview. This will be described later.

The following describes details of optical path lengths of thewaveguides constituting the first arrayed waveguide 103 of the arrayedwaveguide diffraction grating according to the embodiment. When adifference between optical path lengths of adjacent waveguides of thefirst arrayed waveguide 103 is represented by ΔL, a center wavelength λ₀of the arrayed waveguide diffraction grating is expressed by thefollowing expression (1). The center wavelength λ₀ is usually thetransmission center wavelength of the center port among output ports ofthe arrayed waveguide diffraction grating. In expression (1), n_(c)represents an effective refractive index of the arrayed waveguide and mrepresents a diffraction order.

In this example, as counted from the upper side of the sheet of FIG. 1 ,an output end of the uppermost first output waveguide 107 will bereferred to as a port 1, an output end of the second first outputwaveguide 107 will be referred to as a port 2, an output end of thethird first output waveguide 107 will be referred to as a port 3, anoutput end of the fourth first output waveguide 107 will be referred toas a port 4, an output end of the fifth first output waveguide 107 willbe referred to as a port 5, an output end of the sixth first outputwaveguide 107 will be referred to as a port 6, an output end of theseventh first output waveguide 107 will be referred to as a port 7, andan output end of the eighth first output waveguide 107 will be referredto as a port 8.

Expression (1)

$\begin{matrix}{\lambda_{0} = \frac{n_{c}\Delta L}{m}} & (1)\end{matrix}$

Also, the free spectral range (FSR) of the arrayed waveguide diffractiongrating is expressed by the following expression (2).

Expression (2)

$\begin{matrix}{{FSR} \cong \frac{\lambda_{0}}{m}} & (2)\end{matrix}$

As for expressions (1) and (2), refer to Reference Documents 2 and 3.

It is possible to cover all the wavelength regions of theabove-described access-type PON systems by setting the free spectralrange (FSR) of the arrayed waveguide diffraction grating to at least 400nm of from 1250 nm to 1650 nm, setting the center wavelength λ₀ to 1450nm, setting wavelength intervals to 50 nm, and setting the number offirst output waveguides 107 to eight, for example. In this case, thecenter wavelength of the FSR is 1450 nm, and accordingly, thediffraction order m can be set to any of 1 to 3 according to expression(2).

Here, according to expression (1), the optical path length difference ΔLis a very small length on the order of μm, and cannot be realized withan arcuate structure in which the first arrayed waveguide 103 is curvedonly at a single point. Therefore, in the embodiment, the first arrayedwaveguide 103 is curved at a plurality of points in a center portion andin portions (both side portions) on both sides of the center portion ina plan view. By providing a plurality of curved portions as describedabove, it is possible to make the optical path length change from theupper side (outer side) toward the lower side (inner side) of the sheetof FIG. 1 inversely at different curved portions of the first arrayedwaveguide 103.

For example, the first arrayed waveguide 103 is curved outward at thecenter portion in a plan view, and is curved inward at both sideportions of the center portion in the plan view. In this configuration,the optical path length increases toward the outer side (upper side ofthe sheet of FIG. 1 ) in the center portion of the first arrayedwaveguide 103, but decreases toward the outer side in both sideportions. It is possible to set a very small difference in optical pathlength in the entire first arrayed waveguide 103 by setting differentvalues for a difference in optical path length between adjacentwaveguides in the center portion of the first arrayed waveguide 103 anda difference in optical path length between adjacent waveguides in bothside portions to counterbalance changes in the optical path length inthe center portion and both side portions to some extent. Details ofdesign of the above-described difference in optical path length aredescribed in Reference Document 1.

A function of the transmission spectrum of the arrayed waveguidediffraction grating (optical waveguide chip 101) is expressed by aGaussian function. FIG. 4 shows a calculation result example. Thetransmission center wavelength of the output port 1 is 1275 nm. Thetransmission center wavelength of the output port 2 is 1325 nm. Thetransmission center wavelength of the output port 3 is 1375 nm. Thetransmission center wavelength of the output port 4 is 1425 nm. Thetransmission center wavelength of the output port 5 is 1475 nm. Thetransmission center wavelength of the output port 6 is 1525 nm. Thetransmission center wavelength of the output port 7 is 1575 nm. Thetransmission center wavelength of the output port 8 is 1625 nm.

The function of the transmission spectrum will be described. When lossis ignored, a transmission function of the arrayed waveguide diffractiongrating can be expressed by expression (3) (see Reference Document 3).

Expression (3)

$\begin{matrix}{{T\left( {\delta f} \right)} = {\exp\left\{ {- \left( \frac{\Delta x\delta f}{\omega_{0}\Delta f} \right)^{2}} \right\}}} & (3)\end{matrix}$

In expression (3), δf represents a deviation from a transmission centerfrequency, Δx represents an interval between center positions of thefirst output waveguides 107 connected to the first output-side slabwaveguide 105, Δf represents an interval between center frequencies ofadjacent channels, and ω₀ represents a spot size.

Here, when a deviation from the transmission center wavelength isrepresented by δλ and an interval between center wavelengths of adjacentchannels is represented by Δλ, the following expression (4) holds true,and expression (5) is obtained by substituting expression (4) intoexpression (3). Expression (3) that is expressed in the frequency domainis expressed in the wavelength domain by expression (5).

Expressions (4) and (5)

$\begin{matrix}{\frac{\delta\lambda}{\Delta\lambda} = \frac{\delta f}{\Delta f}} & (4)\end{matrix}$ $\begin{matrix}{{T\left( {\delta\lambda} \right)} \cong {\exp\left\{ {- \left( \frac{\Delta x\delta\lambda}{\omega_{0}\Delta\lambda} \right)^{2}} \right\}}} & (5)\end{matrix}$

FIG. 4 shows a result of calculating the transmission spectrum of eachchannel of the arrayed waveguide diffraction grating using expression(5). Note that a parameter Δx/ω₀ that represents steepness of theGaussian function can be adjusted when the arrayed waveguide diffractiongrating is designed, and the parameter Δx/ω₀ is set to 4.5 in theembodiment.

Incidentally, the wavelength range is as wide as from 1250 nm to 1650nm, and accordingly, in the arrayed waveguide diffraction gratingdesigned as described above, there is a loss around 1380 nm, forexample, due to absorption by an OH group in the quartz glassconstituting the waveguides. However, this wavelength band is not usedfor transmission, and therefore does not affect operationcharacteristics of the arrayed waveguide diffraction grating.Calculation regarding the absorption by the OH group in the quartz glassconstituting the waveguides is not taken into account in the calculationresult shown in FIG. 4 .

Also, the above-described arrayed waveguide diffraction grating has achannel interval of 50 nm, and temperature dependence of demultiplexingwavelength of an interference filter in which quartz-based waveguidesare used is 0.01 nm/° C. Even when it is assumed that the temperature ofan environment in which the arrayed waveguide diffraction grating isused changes by 40° C. from −5° C. to 35° C. between cases where thegrating is used outdoors and indoors, according to the above-describedtemperature dependence, a wavelength variation is about 0.4 nm, which isno greater than 1/100 of the interval between adjacent channels and doesnot affect demultiplexing characteristics. Therefore, it is notnecessary to control temperature using a Peltier element or the likewhen the above-described arrayed waveguide diffraction grating isactually used.

Also, in the case of quartz-based waveguides, TE/TM polarizationdependence of the transmission spectrum is about 0.1 to 0.2 nm, but inthe arrayed waveguide diffraction grating, the interval between adjacentchannels, i.e., resolution is as large as 50 nm, and therefore thepolarization dependence is negligible.

Embodiment 2

Next, a wavelength checker according to Embodiment 2 of the presentinvention will be described with reference to FIGS. 5A, 5B, and 5C.

The wavelength checker includes the optical waveguide chip 101. Theoptical waveguide chip 101 is the same as that in Embodiment 1 describedabove. The wavelength checker also includes an optical waveguide chip121 that is arranged next to the optical waveguide chip 101 and includesoptical waveguides that guide outgoing light. A plurality of linearoptical waveguides are formed in the optical waveguide chip 121. Forexample, eight linear optical waveguides that correspond to the eightoutput waveguides of the optical waveguide chip 101 are formed in theoptical waveguide chip 121. Also, the eight linear optical waveguidesare arranged at 1 mm intervals, which are the same as intervals betweenoutput ends of the eight output waveguides of the optical waveguide chip101.

In Embodiment 2, the light conversion portion 102 is arranged at theoutput end 108 of the optical waveguide chip 101 or in the vicinity ofthe output end 108 of the optical waveguide chip 101 on the inner sideof the output end 108. The light conversion portion 102 is the same asthat in Embodiment 1 described above. For example, the light conversionportion 102 can be formed by applying the conversion material thatconverts infrared light to visible light to the output end 108. Also,the optical waveguide chip 121 is arranged next to the optical waveguidechip 101 in series in a wave guiding direction.

In Embodiment 2, the optical waveguide chip 101 and the opticalwaveguide chip 121 are mounted on an optical waveguide chip 141. Thatis, the optical waveguide chips are stacked in two layers. The loweroptical waveguide chip is defined as a parent optical waveguide chip andthe upper optical waveguide chips are defined as child optical waveguidechips. Accordingly, hereinafter, the optical waveguide chips will bereferred to as the child optical waveguide chip 101, the child opticalwaveguide chip 121, and the parent optical waveguide chip 141. A planarlight wave circuit may be formed in the parent optical waveguide chip141, but a configuration is also possible in which the parent opticalwaveguide chip 141 does not include an optical circuit (only clad glassis provided on a Si substrate). The child optical waveguide chip 101 andthe optical waveguide chip 121 are mounted on the parent opticalwaveguide chip 141 with spacers (not shown) interposed therebetween,such that surfaces (surfaces constituted by clad glass) in which opticalwaveguides (planar light wave circuits) are formed face the parentoptical waveguide chip 141 (a surface thereof constituted by cladglass).

Here, optical waveguide chips through which light is passed are thechild optical waveguide chips. When the surfaces constituted by cladglass are referred to as front surfaces, rear surfaces of the childoptical waveguide chips, which are constituted by Si substrates, can beseen from above. That is, in each of the child optical waveguide chips,an optical circuit portion that is constituted by cores and a clad layeris on the lower side. Also, the parent optical waveguide chip 141 ismounted on the main substrate 151. For example, the parent opticalwaveguide chip 141 is fixed on the main substrate 151 by being bondedwith an adhesive. The child optical waveguide chips 101 and 121 arearranged side by side along the direction in which light is input.

Note that the fiber block 161 is connected to an input waveguide end ofthe child optical waveguide chip 101. The optical fiber 162 providedwith the connector 163 for inputting an optical signal that is to bechecked is connected to the fiber block 161. Note that another opticalfiber (not shown) provided with a connector is used for alignmentbetween the fiber block 161 and the input waveguide of the child opticalwaveguide chip 101. Also, the child optical waveguide chip 101 is fixedby being bonded to the parent optical waveguide chip 141 with anadhesive via spacers (not shown) interposed therebetween. On the otherhand, the child optical waveguide chip 121 is in a semi-fixed state andis attachable to and detachable from the parent optical waveguide chip141 and can be replaced.

Here, positioning of the child optical waveguide chips 101 and 121 onthe parent optical waveguide chip 141 will be described with referenceto FIGS. 6A and 6B. First, a plurality of first grooves 131 are formedin the parent optical waveguide chip 141, and second grooves 132 areformed in the child optical waveguide chips 101 and 121. A plurality ofspacer members 171 are fitted in the first grooves 131 such thatportions of the spacer members 171 protrude from the parent opticalwaveguide chip 141. The second grooves 132 in the child opticalwaveguide chip 101 and the second grooves 132 in the child opticalwaveguide chip 121 are each fitted on a protruding portion of any of thespacer members 171. Note that positions of the second grooves 132 areset so as to avoid waveguide portions (cores) of the child opticalwaveguide chips 101 and 121. The number of grooves can be usually set toat least three.

The first grooves 131 are formed in a clad layer 143 of the parentoptical waveguide chip 141. The first grooves 131 are formed so as toextend through the clad layer 143 and reach a substrate 142. Similarly,the second grooves 132 are formed in a clad layer 124 of the childoptical waveguide chip 121 that includes cores 123. The second grooves132 are formed so as to extend through the clad layer 124 and reach asubstrate 122.

The first grooves 131 and the second grooves 132 can be formed using aknown photolithography technique and etching technique (reactive ionetching or the like). The first grooves 131 are formed by etching theclad layer 143 by using a mask pattern formed using the photolithographytechnique as a mask, and using the substrate 142 as an etching stoplayer. Similarly, the second grooves 132 are formed by etching the cladlayer 124 by using a mask pattern formed using the photolithographytechnique as a mask, and using the substrate 122 as an etching stoplayer.

Position accuracy (displacement amount) in in-plane directions of thefirst grooves 131 and the second grooves 132 formed as described abovewith respect to designed positions is determined by position accuracy ofthe mask pattern and an amount of displacement during etching. As iswell known, the position accuracy of the mask pattern is submicron orless, and the amount of displacement during reactive ion etching is alsosubmicron or less. Accordingly, the positions of the first grooves 131and the second grooves 132 in in-plane directions are within 1 μm orless from the designed positions.

Also, the depth of the first grooves 131 is determined by the thicknessof the clad layer 143, and the depth of the second grooves 132 isdetermined by the thickness of the clad layer 124. Accuracy of thethicknesses of the clad layers 143 and 124 is determined on the order ofsubmicron with use of a well-known glass deposition technique, forexample. Similar can be said for positions in the thickness direction ofthe cores 123 that are embedded in the clad layer 124.

Here, the spacer members 171 can be formed by cutting an optical fiberinto a predetermined length, for example, and accuracy of the diameterof each spacer member 171 can be determined on the order of submicron.Accordingly, position accuracy of the child optical waveguide chip 121in the thickness direction is also determined within a range of 1 μm orless.

For the reasons described above, it is possible to exactly matchpositions of core centers of corresponding waveguides of the childoptical waveguide chip 101 and the child optical waveguide chip 121mounted on the parent optical waveguide chip 141. Note that positioningbetween a plurality of child chips that are mounted on a parent opticalchip as described above is commonly performed in a state where each chipis not warped. For more detailed descriptions, refer to ReferenceDocuments 4, 5, and 6. This optical mounting configuration is calledPPCP (Pluggable Photonic Circuit Platform). The child optical waveguidechip 121 mounted according to the PPCP is characterized in that the chipis attachable and detachable. Therefore, it is possible to use childoptical waveguide chips 121 having various functions by replacing thechips to flexibly impart the various functions. In other words, the PPCPcan be said to have a characteristic of an optical circuit (opticalchip) version of an electronic block.

Next, manufacture of the child optical waveguide chip 121 will bedescribed with reference to FIGS. 7A to 7E.

First, as shown in FIG. 7A, the substrate 122 that is constituted by Siis prepared. Next, as shown in FIG. 7B, a lower clad layer 124 a isformed on the substrate 122, and a core formation layer 301 is formed onthe lower clad layer 124 a.

The lower clad layer 124 a and the core formation layer 301 can beformed using a flame hydrolysis deposition (FHD) method, for example.First, raw material gas (main component: tetrachlorosilicon) is passedthrough oxyhydrogen flame to deposit thermally hydrolyzed glassmicroparticles on the substrate 122 and form a first microparticle layerthat is to be converted to the lower clad layer 124 a. Subsequently,glass microparticles having a different composition are deposited on thefirst microparticle layer by changing the composition of the rawmaterial gas (changing the concentration of GeO₂ dopant) to form asecond microparticle layer that is to be converted to the core formationlayer 301. Thereafter, the first microparticle layer and the secondmicroparticle layer are heated using an electric furnace or the like,for example, to convert each of the layers to a transparent film havinga glass composition, and thus the lower clad layer 124 a and the coreformation layer 301 are obtained. Note that these layers can also beformed using a chemical vapor deposition method.

Next, the core formation layer 301 is patterned using a knownlithography technique and etching technique that are used in manufactureof semiconductor devices, to form the cores 123 as shown in FIG. 7C. Forexample, a resist pattern is formed on portions of the core formationlayer 301 that are to be used as the cores 123, by usingphotolithography technique. Next, the core formation layer 301 is etchedby reactive ion etching (RIE) using the formed resist pattern as a maskto leave the portions to be used as the cores 123 and remove the otherportions of the core formation layer. Thereafter, the resist pattern isremoved, and thus the cores 123 are formed.

Next, as shown in FIG. 7D, an upper clad layer 124 b, is formed on thecores 123. Similarly to the lower clad layer 124 a described above, theupper clad layer 124 b, can be formed using the FHD method.

Next, the upper clad layer 124 b and the lower clad layer 124 a arepatterned using a known lithography technique and etching technique toform the second grooves 132 that extend through the upper clad layer 124b, and the lower clad layer 124 a and reach the substrate 122 as shownin FIG. 7E. For example, a resist pattern that includes openings atpositions at which the second grooves 132 are to be formed is formed onthe upper clad layer 124 b by using a photolithography technique. Next,the upper clad layer 124 b, and the lower clad layer 124 a are etched bythe RIE using the formed resist pattern as a mask to remove portions atwhich the second grooves 132 are to be formed. Thereafter, the resistpattern is removed, and thus the second grooves 132 are formed. Inparticular, the substrate 122 is constituted by Si, and therefore servesas an etching stop layer when a layer that is constituted byquartz-based glass is processed by the RIE.

FIGS. 8A and 8B show enlarged cross sections of an emission portion ofthe child optical waveguide chip 121. FIG. 8A shows a configuration inwhich the light conversion portion 102 is provided on a surface of theoutput end 108 of the optical waveguide chip 101, and the reflectionfilm 109 b is provided on the sloped surface of the reflection portion109 that is constituted by a prism. FIG. 8B shows a configuration inwhich the output end 108 is recessed from the output end 108 side endportion of the Si substrate iii, the light conversion portion 102 isprovided at the output end 108 on the end portion of the Si substrateiii, and the fixing member 102 a made of a transparent material such asglass is additionally provided. In FIG. 8B as well, the reflection film109 b is provided on the sloped surface of the reflection portion 109constituted by a prism.

Here, assume that light is guided through the optical waveguides with amode field diameter (MFD) of 6 μm (=spot size of 3 μm), for example.This mode field diameter corresponds approximately to a mode fielddiameter that is realized with an optical waveguide of which the corehas a cross section of 4.5 μm×4.5 μm (rectangular) and in which arelative refractive index difference between the core and the clad is1.5%, for example. Note that the spot size is half the MFD.

When light having the MFD of 6 μm is emitted from an end surface (outputend 108), the beam spreads due to diffraction. In the following, thespread of the beam will be calculated by approximating an electric fielddistribution within the optical waveguide to a Gaussian distribution.Note that light (beam) that is guided through the child opticalwaveguide chip 121 and converted to visible light by the lightconversion portion 102 is reflected by the reflection film 109 b towardthe upper side of the main substrate 151.

When the spot size at the emission end is represented by ω₀, a diameterof the beam that has propagated by a distance of z from the emission endsurface is expressed by expression (6). Details of this are described inReference Document 7. In expression (6), λ represents the wavelength.Under conditions where the squared term in √ in expression (6) issufficiently larger than 1 (in this case, z>about 100 μm), expression(6) can be approximated to expression (7).

Expressions (6) and (7)

$\begin{matrix}{{\omega(z)} = {\omega_{0}\sqrt{1 + \left( \frac{\lambda z}{\pi\omega_{0}^{2}} \right)^{2}}}} & (6)\end{matrix}$ $\begin{matrix}{{\omega(z)} \cong {\omega_{0}\left( \frac{\lambda z}{\pi\omega_{0}^{2}} \right)}} & (7)\end{matrix}$

FIG. 9 shows a graph obtained by plotting expression (7). According toexpression (7), it can be found that when light (beam) has propagated bya distance of about 6 mm, the spot size is 1000 mμm, and the MFD is 2mm, which is the same as the waveguide pitch.

Note that, in the wavelength checker according to Embodiment 2 describedusing FIGS. 5A, 5B, and 5C, the transmission spectrum of the childoptical waveguide chip 121 is the same as that in Embodiment 1, and thespectrum shown in FIG. 4 is obtained.

Incidentally, as shown in FIG. 10 , it is also possible to use a childoptical waveguide chip 121 a that includes an arrayed waveguidediffraction grating, in place of the child optical waveguide chip 121.The child optical waveguide chip 121 a includes the arrayed waveguidediffraction grating that has a narrow interval between demultiplexingwavelengths. In FIG. 10 , the reference sign 125 denotes a secondarrayed waveguide, the reference sign 126 denotes a second input-sideslab waveguide, the reference sign 127 denotes a second output-side slabwaveguide, the reference sign 128 denotes a second input waveguide, andthe reference sign 129 denotes second output waveguides. This is anordinary arrayed waveguide diffraction grating in which the secondarrayed waveguide 125 has an arcuate shape in a plan view. The arrayedwaveguide diffraction grating has demultiplexing wavelengths from 1550nm to 1600 nm, a demultiplexing wavelength interval of 5 nm, and tenports. In FIG. 10 , some of the second output waveguides 129 areomitted.

FIG. 11 shows a state of connection between the child optical waveguidechip 101 and the child optical waveguide chip 121 a. The followingconsiders a case where the second input waveguide 128 of the childoptical waveguide chip 121 a is optically connected to the port 7 of thefirst output waveguides 107 of the child optical waveguide chip 101 asshown in FIG. 11 . FIG. 12 shows a transmission wavelength spectrum ofthe arrayed waveguide diffraction grating (having the narrowdemultiplexing wavelength interval) of the child optical waveguide chip121 of this case. This spectrum is a result of calculation performedusing expression (5). On the other hand, the transmission spectrum ofthe arrayed waveguide diffraction grating of the child optical waveguidechip 101 is a broad spectrum as shown in FIG. 13 . The transmissionspectrum of the configuration in which the child optical waveguide chip101 and the child optical waveguide chip 121 a are connected is acomposite of the spectrum shown in FIG. 12 and the spectrum shown inFIG. 13 and is shown in FIG. 14 .

In the case where the child optical waveguide chip 121 constituted bythe linear optical waveguides is combined with the child opticalwaveguide chip 101, the transmission spectrum is as shown in FIG. 4 ,and the wavelength resolution is 50 nm. In contrast, in the transmissionspectrum of the case where the child optical waveguide chip 121 aconstituted by the arrayed waveguide diffraction grating is combinedwith the child optical waveguide chip 101, the wavelength resolution is5 nm, and it can be understood that the wavelength can be checked moreprecisely.

Also, in the configuration in which the child optical waveguide chip 121is combined with the child optical waveguide chip 101, the measurementrange is from 1250 nm to 1650 nm and is as wide as 400 nm as shown inFIG. 4 . In contrast, in the configuration in which the child opticalwaveguide chip ma is combined with the child optical waveguide chip 101,the measurement range is narrow as shown in FIG. 14 .

As described above, by mounting the child optical waveguide chips 121and 121 a according to the PPCP so as to be replaceable with each other,it is possible to flexibly change the wavelength resolution and themeasurement range of the wavelength checker.

In the above-described case, the wavelength is precisely checked withrespect to the wavelength range from 1550 nm to 1600 nm by using thearrayed waveguide diffraction grating having the narrow wavelengthinterval, but it can be understood that it is possible to check thewavelength with the wavelength resolution of 5 nm in another wavelengthrange as well by preparing an arrayed waveguide diffraction grating thathas 10 ports at 5 nm intervals corresponding to a wavelength range ofanother output port of the arrayed waveguide diffraction grating of thechild optical waveguide chip 101, and by connecting the prepared arrayedwaveguide diffraction grating to the output port.

Here, the arrayed waveguide diffraction grating having the narrowdemultiplexing wavelength interval will be additionally described. Anarrayed waveguide diffraction grating of which the free spectral range(FSR) is equal to a product of the channel interval and the number ofchannels is called a cyclic arrayed waveguide diffraction grating. Ifthe cyclic arrayed waveguide diffraction grating is used as the arrayedwaveguide diffraction grating having the narrow wavelength interval, thesame cyclic arrayed waveguide diffraction grating can be shared as anoptical chip to be connected to the child optical waveguide chip 101.However, the arrayed waveguide diffraction grating cannot be sharedbetween channels of which wavelengths are too far, such as the 1500 nmband and the 1300 nm band, because a refractive index differenceincreases due to influence of refractive index dispersion.

Although a device structure of the wavelength checker has been describedabove, the following gives a supplementary description from thestandpoint of a wavelength inspection method. As a method for inspectingthe wavelength in an access-type PON system, it is possible to proposean inspection method of demultiplexing light according to wavelengths bythe arrayed waveguide diffraction grating, emitting the demultiplexedlight toward a material (wavelength conversion material) that convertsnear infrared light to visible light, and checking the wavelength byseeing a port from which light is emitted. A broad interpretation of thearrayed waveguide diffraction grating is a diffraction grating(grating), and accordingly, it is also possible to propose an inspectionmethod of demultiplexing light according to wavelengths by thediffraction grating (grating), emitting the demultiplexed light towardthe wavelength conversion material, and checking the wavelength byseeing a position from which light is emitted. These inspection methodsare characterized in that wavelength inspection can be easily performedwithout using a power source or the like.

Embodiment 3

Next, a wavelength checker according to Embodiment 3 of the presentinvention will be described with reference to FIG. 15 . In Embodiment 3,a child optical waveguide chip 101 a shown in FIG. 15 is used instead ofthe child optical waveguide chip 101 in the wavelength checker describedusing FIGS. 5A, 5B, and 5C. In the child optical waveguide chip Iola, amain first input waveguide 106 a and a sub first input waveguide 106 bare connected to the input side of the first input-side slab waveguide104. The other configurations are the same as those in the child opticalwaveguide chip 101, and the child optical waveguide chip 101 a isconstituted by a plurality of linear optical waveguides.

Here, when a waveguide interval between portions of the plurality offirst output waveguides 107 that are connected to the first output-sideslab waveguide 105 is represented by Δx_(out), a waveguide intervalbetween a portion of the main first input waveguide 106 a that isconnected to the first input-side slab waveguide 104 and a portion ofthe sub first input waveguide 100 that is connected to the firstinput-side slab waveguide 104 is Δx_(out)/2. Also, in the child opticalwaveguide chip 101 a, shapes of the first input-side slab waveguide 104,the first arrayed waveguide 103, and the first output-side slabwaveguide 105 in a plan view are symmetrical with respect to a straightline that extends through the middle point of a line segment connectingthe center of the first input-side slab waveguide 104 and the center ofthe first output-side slab waveguide 105 and that is perpendicular tothe line segment. The side of the first input-side slab waveguide 104that is in contact with the input waveguides and the side of the firstinput-side slab waveguide 104 that is in contact with the arrayedwaveguide are arcs having the same curvature. Therefore, the center ofthe input-side slab waveguide is an intersection point between straightlines that diagonally connect four points at which straight lines andthe arcs that constitute the external shape of the slab waveguideintersect. Similar can be said for the first output-side slab waveguide105.

The following describes more details.

The main first input waveguide 106 a is connected to the center of thefirst input-side slab waveguide 104. Assume that the first outputwaveguides 107 are connected at the waveguide interval Δx_(out) withrespect to the center of the first output-side slab waveguide 105, andtransmission center wavelengths of the respective first outputwaveguides 107 are set at equal wavelength intervals to λ1, λ2, λ3, . .. , and λ8. Also, the sub first input waveguide 106 b is connected tothe first input-side slab waveguide 104 at a waveguide interval ofΔx=Δx_(out) with respect to the main first input waveguide 106 a (seeFIGS. 16A and 168 ).

If the shapes of the first input-side slab waveguide 104, the firstarrayed waveguide 103, and the first output-side slab waveguide 105 in aplan view are symmetrical as described above, the following holds true.

When the sub first input waveguide 106 b is connected so as to beshifted from the main first input waveguide 106 a,wavelength-division-multiplexed light that is input to the sub firstinput waveguide 106 b is separated at equal intervals such thattransmission center wavelengths of the first output waveguides 107 areλ2, λ3, λ4, . . . , and λ9. This is because, due to the sub first inputwaveguide 106 b being shifted by an amount corresponding to a singlewaveguide, a wavefront that reaches the first arrayed waveguide 103 isinclined and consequently, a wavefront that reaches the first outputwaveguides 107 is inclined, and light having the same wavelength iscollected to a first output waveguide 107 that is next to the firstoutput waveguide 107 to which the light is collected when input to themain first input waveguide.

In the arrayed waveguide diffraction grating, there is a linearrelationship between a position of connection between the slab waveguideand the input waveguide and the transmission center wavelength. Detailsare described in Reference Document 8. Accordingly, when the waveguideinterval between the main first input waveguide 106 a and the sub firstinput waveguide 106 b is Δx=Δx_(out)/2 and an interval between centerwavelengths of adjacent channels is represented by Δλ, the transmissioncenter wavelengths are λ1+Δλ/2, λ2+Δλ/2, λ3+Δλ/2, . . . , and λ8+Δλ/2.Note that Δλ=λ2−λ1=λ3−λ2= . . . =λ9−λ8.

When the arrayed waveguide diffraction grating of the child opticalwaveguide chip 101 a is designed similarly to the child opticalwaveguide chip 101, the spectrum (calculation value) of light that isinput from the main first input waveguide 106 a and is transmittedthrough the arrayed waveguide diffraction grating is the same as thetransmission spectrum of the child optical waveguide chip 101 as shownin FIG. 17A. That is, the transmission center wavelengths of the firstoutput waveguides 107 are 1275 nm, 1325 nm, 1375 nm, 1425 nm, 1475 nm,1525 nm, 1575 nm, and 1625 nm.

On the other hand, the spectrum (calculation value) of light that isinput from the sub first input waveguide 100 and is transmitted throughthe arrayed waveguide diffraction grating is shifted by half thewavelength interval and the transmission center wavelengths are 1300 nm,1350 nm, 1400 nm, 1450 nm, 1500 nm, 1550 nm, 1600 nm, and 1650 nm asshown in FIG. 17B. That is, the transmission spectrum of the light inputfrom the main first input waveguide 106 a and the spectrum of the lightinput from the sub first input waveguide 100 alternate with each other.

When compared with a case where a single input waveguide is provided forthe arrayed waveguide diffraction grating, the configuration in whichthe main first input waveguide 106 a and the sub first input waveguide100 are provided has the following effects. In the case where the singleinput waveguide is provided, when light having a wavelength that isbetween transmission spectrums of adjacent first output waveguides 107is input, transmittance is low, and accordingly, visible light convertedfrom the near infrared light is weak, and the light emitted from thelight conversion portion 102 may not be recognized.

For example, transmitted light intensities of the ports 1 and 2 at awavelength of 1300 nm in FIG. 17A are lower by 20 dB than that atwavelengths (1275 nm and 1325 nm) at which transmittance is the highest.

In contrast, in the case where the main first input waveguide 106 a andthe sub first input waveguide 100 are used, when signal light is alsoinput to the sub first input waveguide 106 b, the transmitted lightintensity of the port 1 at the wavelength of 1300 nm is that atwavelengths at which transmittance is the highest. As a result, as shownin FIG. 18 in which FIGS. 17A and 17B are superposed, when the mainfirst input waveguide 106 a and the sub first input waveguide 100 areused, a reduction in the transmitted light intensity is only 5 dB evenat wavelengths at which the transmittance is the lowest, when comparedwith the transmitted light intensity at wavelengths at which thetransmittance is the highest.

Therefore, even if the wavelength cannot be recognized due to thetransmitted light intensity of signal light being low when the signallight is input to a single input waveguide, if the signal light is inputto both the main first input waveguide 106 a and the sub first inputwaveguide 106 b, stronger light is emitted from the light conversionportion 102 and the wavelength can be recognized more reliably.

As described above, according to embodiments of the present invention,the reflection portion is provided at a position at which the reflectionportion faces the light emission end surface, and the light conversionportion constituted by the conversion material that converts infraredlight to visible light is arranged at the light emission end surface ofthe optical waveguide chip or in the vicinity of the light emission endsurface of the optical waveguide chip on the inner side of the lightemission end surface, and therefore, it is possible to easily check thepresence or absence of signal light when starting a PON system orisolating a failure in the PON system, for example.

The present invention is not limited to the embodiments described above,and it is apparent that a person having ordinary skill in the art canmake many modifications and combinations within the technical idea ofthe present invention.

[Reference Document 1] Japanese Patent Application Publication No.H10-104446

[Reference Document 2] Hiroshi Takahashi, et al., “Arrayed WaveguideDiffraction Grating for WDM”, NIT R&D, vol. 46, no. 7, pp. 685-692,1997.

[Reference Document 3] H. Takahashi et al., “TransmissionCharacteristics of Arrayed Waveguide N×N Wavelength Multiplexer”,Journal of Lightwave Technology, vol. 13, no. 3, pp. 447-455, 1995.

[Reference Document 4] Japanese Patent Application Publication No.2017-32950.

[Reference Document 5] H. Ishikawa et al., “Pluggable Photonic CircuitPlatform Using a Novel Passive Alignment Method”, The Japan Society ofApplied Physics, 22nd Microoptics Conference, D-6, pp. 84-85, 2017.

[Reference Document 6] K. Shikama et al., “Pluggable photonic circuitplatform for single-mode waveguide connections using novel passivealignment method”, Japanese Journal of Applied Physics, vol. 57, 08PC03,2018.

[Reference Document 7] Kenji Kawano, “Basics and Applications of OpticalCoupling System for Optical Device”, Gendai Kougaku-sha, first edition,1991.

[Reference Document 8] H. Takahashi et al., “Wavelength MultiplexerBased on SiO₂—Ta₂O₅ Arrayed-Waveguide Grating”, IEEE Journal ofLightwave Technology, vol. 12, no. 6, pp. 989-005, 1994.

REFERENCE SIGNS LIST

-   -   101 Optical waveguide chip    -   102 Light conversion portion    -   103 First arrayed waveguide    -   103 a Core portion    -   104 First input-side slab waveguide    -   104 a Core portion    -   105 First output-side slab waveguide    -   106 First input waveguide    -   106 a Main first input waveguide    -   106 b Sub first input waveguide    -   107 First output waveguide    -   108 Output end    -   109 Reflection portion    -   109 a Reflection surface    -   109 b Reflection film    -   111 Si substrate    -   112 Lower clad layer    -   113 Upper clad layer    -   120 a Optical waveguide portion    -   120 b Arrayed waveguide diffraction grating    -   121 Optical waveguide chip    -   121 a Child optical waveguide chip    -   121 b Child optical waveguide chip    -   122 Substrate    -   123 Core    -   124 Clad layer    -   124 a Lower clad layer    -   124 b Upper clad layer    -   125 Second arrayed waveguide    -   126 Second input-side slab waveguide    -   127 Second output-side slab waveguide    -   128 Second input waveguide    -   129 Second output waveguide    -   131 First groove    -   132 Second groove    -   141 Optical waveguide chip    -   142 Substrate    -   143 Clad layer    -   151 Main substrate    -   161 Fiber block    -   162 Optical fiber    -   163 Connector    -   171 Spacer member    -   501 Arrayed waveguide    -   502 Input-side slab waveguide    -   503 Output-side slab waveguide    -   504 Input waveguide    -   505 Output waveguide

1-7. (canceled)
 8. A wavelength checker comprising: an optical waveguidechip mounted on a main substrate and connected to an optical fiber, theoptical waveguide chip comprising an arrayed waveguide diffractiongrating; a reflection portion fixed to a position on the main substrateat which the reflection portion faces a light emission end surface ofthe optical waveguide chip on a side from which light is output to anexternal space, the reflection portion comprising a reflection surfacethat faces the light emission end surface and is inclined with respectto a plane of the main substrate such that a reflection direction istoward an upper side of the main substrate; and a light conversionportion comprising a conversion material configured to convert nearinfrared light to visible light, wherein the light conversion portion isarranged adjacent to the light emission end surface of the opticalwaveguide chip.
 9. The wavelength checker according to claim 8, whereinthe light conversion portion is arranged adjacent to an inner side ofthe light emission end surface in a groove provided across opticalwaveguides that extend to the light emission end surface of the opticalwaveguide chip.
 10. The wavelength checker according to claim 8, whereinthe reflection portion comprises a right-angle prism that includes asloped surface on which a reflection film that reflects the nearinfrared light is provided as the reflection surface.
 11. The wavelengthchecker according to claim 8, wherein: a plurality of the opticalwaveguide chips are stacked in two layers; each of the optical waveguidechips comprises a substrate, and a core and a clad provided on thesubstrate; when a clad side of each of the optical waveguide chips isdefined as a front surface of the optical waveguide chip, a frontsurface of an upper optical waveguide chip faces a front surface of alower optical waveguide chip; when the lower optical waveguide chip isdefined as a parent optical waveguide chip, and the upper opticalwaveguide chip is defined as a child optical waveguide chip, thewavelength checker includes the parent optical waveguide chip and aplurality of the child optical waveguide chips; a plurality of firstgrooves are provided in a clad portion of the parent optical waveguidechip and a plurality of second grooves are provided in clad portions ofthe child optical waveguide chips; a plurality of spacer members arerespectively fitted in the plurality of first grooves such that portionsof the spacer members protrude from the parent optical waveguide chip;each of the second grooves of the child optical waveguide chips isfitted on a protruding portion of any of the plurality of spacermembers; the child optical waveguide chip that is connected to theoptical fiber comprises an arrayed waveguide diffraction grating andanother child optical waveguide chip comprises a group of linearwaveguides or an arrayed waveguide diffraction grating; and the parentoptical waveguide chip is fixed on the main substrate.
 12. Thewavelength checker according to claim 11, wherein the spacer memberscomprise additional optical fibers.
 13. The wavelength checker accordingto claim 11, wherein the substrate of each of the optical waveguidechips comprises Si and the core and the clad comprise quartz-basedglass.
 14. The wavelength checker according to claim 8, wherein: aplurality of the optical waveguide chips are stacked in two layers; eachof the optical waveguide chips comprises a substrate and a clad that isprovided on the substrate; when a clad side of each of the opticalwaveguide chips is defined as a front surface of the optical waveguidechip, a front surface of an upper optical waveguide chip faces a frontsurface of a lower optical waveguide chip; when the lower opticalwaveguide chip is defined as a parent optical waveguide chip, and theupper optical waveguide chip is defined as a child optical waveguidechip, the wavelength checker includes the parent optical waveguide chipand a plurality of the child optical waveguide chips; a plurality offirst grooves are provided in a clad portion of the parent opticalwaveguide chip and a plurality of second grooves are provided in cladportions of the child optical waveguide chips; a plurality of spacermembers are respectively fitted in the plurality of first grooves suchthat portions of the spacer members protrude from the parent opticalwaveguide chip; each of the second grooves of the child opticalwaveguide chips is fitted on a protruding portion of any of theplurality of spacer members; the child optical waveguide chip that isconnected to the optical fiber comprises an arrayed waveguidediffraction grating and another child optical waveguide chip comprises agroup of linear waveguides or an arrayed waveguide diffraction grating;and the parent optical waveguide chip is fixed on the main substrate.15. The wavelength checker according to claim 14, wherein the spacermembers comprise additional optical fibers.
 16. The wavelength checkeraccording to claim 14, wherein the substrate of each of the opticalwaveguide chips comprises Si and the clad comprises quartz-based glass.17. The wavelength checker according to claim 8, wherein the conversionmaterial comprises a phosphor.
 18. A method of forming a wavelengthchecker, the method comprising: mounting an optical waveguide chip on amain substrate and connected to an optical fiber, the optical waveguidechip comprising an arrayed waveguide diffraction grating; fixing areflection portion to a position on the main substrate at which thereflection portion faces a light emission end surface of the opticalwaveguide chip on a side from which light is output to an externalspace, the reflection portion comprising a reflection surface that facesthe light emission end surface and is inclined with respect to a planeof the main substrate such that a reflection direction is toward anupper side of the main substrate; and arranging a light conversionportion adjacent to the light emission end surface of the opticalwaveguide chip, the light conversion portion comprising a conversionmaterial that converts near infrared light to visible light.
 19. Themethod according to claim 18, wherein the light conversion portion isarranged adjacent to an inner side of the light emission end surface ina groove provided across optical waveguides that extend to the lightemission end surface of the optical waveguide chip.
 20. The methodaccording to claim 18, wherein the reflection portion comprises aright-angle prism that includes a sloped surface on which a reflectionfilm that reflects near infrared light is provided as the reflectionsurface.
 21. The method according to claim 18, wherein: a plurality ofthe optical waveguide chips are stacked in two layers; each of theoptical waveguide chips comprises a substrate, and a core and a cladprovided on the substrate; when a clad side of each of the opticalwaveguide chips is defined as a front surface of the optical waveguidechip, a front surface of an upper optical waveguide chip faces a frontsurface of a lower optical waveguide chip; when the lower opticalwaveguide chip is defined as a parent optical waveguide chip, and theupper optical waveguide chip is defined as a child optical waveguidechip, the wavelength checker includes the parent optical waveguide chipand a plurality of the child optical waveguide chips; a plurality offirst grooves are provided in a clad portion of the parent opticalwaveguide chip and a plurality of second grooves are provided in cladportions of the child optical waveguide chips; a plurality of spacermembers are respectively fitted in the plurality of first grooves suchthat portions of the spacer members protrude from the parent opticalwaveguide chip; each of the second grooves of the child opticalwaveguide chips is fitted on a protruding portion of any of theplurality of spacer members; the child optical waveguide chip that isconnected to the optical fiber comprises an arrayed waveguidediffraction grating and another child optical waveguide chip comprises agroup of linear waveguides or an arrayed waveguide diffraction grating;and the parent optical waveguide chip is fixed on the main substrate.22. The method according to claim 21, wherein the spacer memberscomprise the optical fiber.
 23. The method according to claim 21,wherein the substrate of each of the optical waveguide chips comprisesSi and the core and the clad comprise quartz-based glass.
 24. The methodaccording to claim 18, wherein: a plurality of the optical waveguidechips are stacked in two layers; each of the optical waveguide chipscomprises a substrate and a clad that is provided on the substrate, whena clad side of each of the optical waveguide chips is defined as a frontsurface of the optical waveguide chip, a front surface of an upperoptical waveguide chip faces a front surface of a lower opticalwaveguide chip; when the lower optical waveguide chip is defined as aparent optical waveguide chip, and the upper optical waveguide chip isdefined as a child optical waveguide chip, the wavelength checkerincludes the parent optical waveguide chip and a plurality of the childoptical waveguide chips; a plurality of first grooves are provided in aclad portion of the parent optical waveguide chip and a plurality ofsecond grooves are provided in clad portions of the child opticalwaveguide chips; a plurality of spacer members are respectively fittedin the plurality of first grooves such that portions of the spacermembers protrude from the parent optical waveguide chip; each of thesecond grooves of the child optical waveguide chips is fitted on aprotruding portion of any of the plurality of spacer members; the childoptical waveguide chip that is connected to the optical fiber comprisesan arrayed waveguide diffraction grating and another child opticalwaveguide chip comprises a group of linear waveguides or an arrayedwaveguide diffraction grating; and the parent optical waveguide chip isfixed on the main substrate.
 25. The method according to claim 24,wherein the spacer members comprise the optical fiber.
 26. The methodaccording to claim 24, wherein the substrate of each of the opticalwaveguide chips comprises Si and the clad comprises quartz-based glass.27. The method according to claim 18, wherein the conversion materialcomprises a phosphor.